Filament for incandescent lamps or other vacuum apparatus



June 9, 1925.

F. SKAUPY ET AL FILAMENT FOR INCANDESCENT LAMPS OR OTHER VACUUM APPARATUS Filed Nov. 5, 1924 Inventors: Franz SKaupy 7 Fritz Koref,

by Their Attorney Patented June 9, 1925 UNITED STATES PATENT OFFICE.

ram SKAUPY Aim'rm'rz xoanr, or 3mm, GERMANY, assrenoas 'ro GENERAL ELECTRIC conamr, a coaroaarron or NEW YORK.

F'ILAHENT FDR INCANDESCEH'I' LAKES OR OTHER ITAOUUE APPARATUS.

Application filed November To all} whom it may comm.-

Be it known that we, FRANZ Smurr and FRITZ Konnr, citizens, respectively, of Austria andof Germany, residing at Berlin,

6 Germany, have invented certam new and useful Improvement. 1 Filaments for Incandescent Lamps or Other Vacuum Apparatus (for which we have filed applications in Germany August 29, 1923, 'P. 46,748

10 VIII/21f (withdrawn); filed in Japan December 8 1923, No. 1,574; filed in Great Britain February 27, 1924, No. 5,060/24 (abandoned) an'amendedcase filed in Germany April 7 1924, P. 48,128 VIII/2H2),

of which the following is a specification.

Our invention relates to filaments for incandescent lamps or' other vacuum devices and the process of its manufacture; More particularly, however, it relates to filaments of the macro-crystal or uni-crystal type.

The details of our invention are hereinafter more fully set forth and claimed, reference being had to the accompanying drawing in which Fig. 1 is a diagrammatic representation of a cross-sectionof the known form of a filament; Fig. 2 is a diagrammatic representation of a cross-section of a new form of filament; Fig. 3 is a diagrammatic representation of a cross-section of another form of filament.

Experiments which have been made with these filaments have demonstrated that the filaments continue to decrease in size the longer they are burned due to the atomization or evaporization of the material. Fig.

1 is the diagrammatic representation of the cross-section of a filament of uni-crystal type which initially is round and which gradually decreases in size, assuming a 40 polygonal cross-section or one with curved surfaces, as indicated by the heavy line a-w in. this figure. In this manner the filament assumes after a period of operation a polygonal shape and the number of surfaces formed depends upon the positions of the long crystals with respect to the axis of the filament. In this manner and after a period of operation also a' polygonal filament can be obtained which has more than four lateral surfaces, six or eight for instance. ;The polygonal or semi-polygonal a, 1924. Serial No. 747578.

cross-section is due the fact that the evaporation does not occur at the same rate over the surface of the filament. -.According to certain crystallographic laws the the line bb where the edges 6 form themselves. On the other hand, the most severe volatilization takes lace along the central part of the surface tween the two edges. As soon as the volatilization of the round filament has reached a sufficient stage, as for instance as far as the surface indicated by the line aa, the volatilization proceeds nearly evenly along the entire sur-' face of the filament. As the volatilization continues the configuration of the cross-section remains approximately the same and for this reason a much greater amount of material is disintegrated within the same time than at, the beginning, as indicated by the fact that the cross-section indicated by the outline a-w is reduced to that indicated by the outline '00. The more the crosssection of the filament varies from the original ,shape the more pronoucnced, becomes the volatilization and therefore the blackeni of the lamp. However, in practice the life of the filament ceases as soon as the polygonal cross-section, which remains constant in shape, is obtained.

According to the invention this fact is made use of in manufacturing filaments which, during the time which the round cross-section changes into the final poly gonal or curve-polygonal cross-section, do not evaporate or atomize to such an extent as the crystal filaments with round cross-- mlnimum volatilization takes place along ment, the part at or nearly at edges of the faces evaporate at a maximum rate whereas the more centrally located parts of the faces are far less subject to evaporation or atomization. As can be seen from Fig. 2 much more time will elapse with the new shape than with the former one until the filament will assume the permanent form of cross-section indicated at heav lines f-f; thus, the blackening of the bu b caused by evaporation or atomization is prevented and the longevity of the filament is increased.

To obtain the desired results the faces of the polygonal filament can be sli I tly curved instead of being straight, as s own in Fig. 2. The lateral area of the filament need not be composed exclusively of faces with minimum rate of evaporation, it is suficient when the latter at least predominate on the surface. For instance, the filament can have a cross-section such as indicated in Fig. 3 where 9 indicates faces of minimum wear and it faces whei'e the wear is more pronounced.

In order to manufacture the new filament, an ordinary round filament may be used to start with which by a preliminary heat treatment is converted into one single crystal or into a number of crystals forming the entire cross-section of the filament. After that the crystal filament is heated in a liquid mixture or in a gaseous atmosphere containing the constituent parts of the filament. In this manner, the' filament increases in size after a certain lapse of time because of the material deposited from the liquid or from the gaseous atmosphere and it assumes automatically a polygonal crosssection. It is thus possible to convert wireshaped round tungsten crystals when heating them in a mixture of hydrogen and tungsten hexachloride into such a polygonal cross-section. Strange to say, it has been found, that a round cylindrical filament grows in a liquid mixture or in the gaseous atmosphere in such a manner that the surfaces that are produced are not parallel but are at an angle to those obtaining during the process of disintegration. In this manner the faces of the filament coincide with the planes where the evaporation is least pronounced;

Filaments of the desired cross-section can also be obtained by causing the filament to become reduced before use, not by evaporation or by atomization, but in the following manner: It has been found that the volatilization of filaments causes them to assume quite different shapes, depending upon the nature of the solvent utilized in the process. For instance, with the tungsten crystals an acid solvent causes a different formation during the reduction than an alkaline solvent. lVith such corrosive solvents and substances or gases, filaments are obtained ably at one end. In this manner, not only i the right position but also the shape of the crystal or crystals before the subsequent grinding can be determined.

What we claim as new and desire to secure by Letters Patent of the United States, is

1. A macro-crystal filament of a refractory metal having a polygonal cross-section in its initial form, which filament when heated reduces to a filament having a second and different form having also a polyg onal cross-section, the filament in the first form having one of its sides in a position at an angle to the position of any of the sides of the filament in its second form.

2. A filament of a refractory metal for producing radiation, said filaments having a polygonal cross-section which when subjected to an electric current reduces to a filament having a different polygonal crosssection, the filament in the first instance having sides in a position at an angle to the sides of the filament in the second instance.

3. A filament of a refractory metal having a polygonal cross-section, said filament so constructed that the central longitudinal zone of one of the surfaces has a minimum rate of evaporation when heated.

4. A filament of a refractory metal having an internal polygonal structure and an external polygonal structure angularly displaced about the longitudinal axis of the filament.

5. A filament of a refractory metal for transmitting radiant energy, said filament having an external polyhedral structure and an internal polyhedral structure, one of the structures having faces sloping with respect to faces of the other structure.

6. A filament of a refractory metal for transmitting radiant energy, said filament having an external polyhedral structure and an internal polyhedral structure, one of the structures having faces sloping with respect to faces of the other structure, the apex lines forming the intersection of adjacent faces of the internal structure extending each parallel to and in proximity of the central longitudinal zone of one of the faces of the external structure.

7. A filament of a refractory metal for transmitting radiant energy, said filament having an external polyhedral structure and an intrnal polyhedral structure, one of the structures having faces sloping With respect to faces of the other structure, the faces of the structures extending in the same direction with the axis of the filament.

8.1K macro-crystal filament for a device for radiating energy having a polygonal cross-section and having surfaces with a relatively low rate of evaporation.

In witness whereof, We have hereunto set 10 our hands this 11th day of 001501121 1924,

FRANZ SKAUPY. mnz KUREF. 

